Recently, the harsh underground conditions pose strict requirements for the transmission of underground sensor data. With the development of measurement-while-drilling technology, how to transmit the underground signal to the ground stably and efficiently has become a vital research subject in the field of drilling. Transmission and reception circuits of all kinds of transmission methods in traditional Computerized Logging System have high power consumption, low transmission efficiency and low anti-electromagnetic interference ability. With the continuous development of optical fiber communication technology, people pay more and more attention to the advantages of optical fiber and apply optical fiber communication in all aspects. The underground communication devices based on optical fiber communication emerged. Optical fiber digital communication technology has become one of the most promising technologies among various communication technologies. Optical fiber digital communication technology combines optical fiber communication, digital communication and network technology to bring all the advantages together. Due to the high frequency of light waves, optical fiber communication has larger capacity and wider bandwidth than ordinary cables, suitable for transmission of the high-speed, broadband information. The loss of the optical fiber is small, can greatly increase distance of the transmission without relay. The optical fiber communication transmits the optical signal, almost never radiates outwardly, and the data security is superior, at the same time it does not suffer crosstalk between the optical fibers in the same optical cable. Also, the optical fiber communication will not be affected by the electromagnetic interference, or produce electric spark and cause safety hazard to oil wells. The anti-explosion properties are good. The raw material of the glass fiber production is quartz, the sources of which are in abundance than the sources of copper, aluminum and other sources for manufacturing cables. The optical fiber is environment friendly, and the service life is long. Optical fiber is a kind of wire communication, long-distance transmission will cause energy loss, and due to different conditions while drilling, some positions are not suitable for transmitting the data by wired method, therefore, the wireless repeaters are used for signal amplification and relay at these position. The principle of the logging cable transmission is to use multi-core cable as a transmission medium, place the multi-core cable inside the drill pipe by embedded method, the transmission link can be set up after the drill pipes are connected and realize the bi-directional communication of the high-speed signals. Various commands and data signals are transmitted by cables between the ground control system and the underground apparatus, the ground-based computer can acquire the position of rig and the sensing information underground. When the sensor of the underground logger collects the data, it modulates the sensing information to digital electrical signal carrier through the digital modulator and sends the sensing information to the ground through the cable. The receiver processes preliminary treatment to the signal through the digital signal processing technology and demodulates the required information thereof. The same method is used for transmitting commands downwards from the ground. Cable transmission is one of the most widely used techniques in logging activity, either in deep wells or in shallow wells. Due to the fact that thicker cable leads to too much internal space of the drill pipe occupied by cable, and its mechanical manufacturing process is relatively complicated. The construction is difficult and the operation is not convenient during the process of on-site drilling. At the same time, cables may face many interference factors in the general logging remote sensing transmission environment. For example, the mineral magnetic materials in some strata will generate certain electromagnetic fields, and some radioactive materials will emit rays, which make the transmission link to be interfered susceptibly and occurrences of aberration or distortion of signal happen, thereby increasing the transmission error rate.
In conclusion, the problems of the existing technologies are as follows: the current drilling communication has the problem that the thicker cable leads to the excessive occupation of the internal space in the drill pipe, and the mechanical manufacturing process is relatively complicated; the construction is difficult and is inconvenient to operate; susceptible to be interfered and the aberration or distortion of signal occurs, the transmission error rate is high.